This invention relates to a gum-resistant catalytic composite particularly adapted to the conversion of mercaptans contained in a sour petroleum distillate. Processes for the treatment of sour petroleum distillates wherein the distillate is treated in contact with a catalyst in the presence of an oxidizing agent at alkaline reaction conditions have become well known and widely practiced in the petroleum refining industry. Said processes are typically designed to effect the oxidation of offensive mercaptans contained in a sour petroleum distillate with the formation of innocuous disulfides--a process commonly referred to as sweetening. Depending on the source of the petroleum from which the sour petroleum distillate was derived, the boiling range of the distillate itself, and the method of processing the petroleum to produce the distillate, the distillates will vary widely with respect to the concentration, molecular weight and complexity of the mercaptans contained therein. For example, in lighter mercaptan-containing petroleum distillates such as straight run gasolines, the mercaptans are primarily lower alkyl mercaptans which are readily oxidized to disulfides. On the other hand, mercaptan-containing gasolines derived from fluid catalytic cracking (FCC) processes are frequently relatively high in olefin content and comprise mercaptans which are more difficult to convert to disulfides, for example, aromatic and higher molecular weight branched chain alkyl mercaptans.
Heretofore, catalytic composites for the conversion of mercaptans contained in sour petroleum distillates were usually prepared by using as a support charcoal particles. Although such composites perform satisfactorily under many circumstances, the use of charcoal has resulted in limitations in the preparation and use of the catalyst. Because charcoal possesses only moderate attrition resistance, methods of preparation and use of the composite which require or result in agitation of the charcoal particles tend to attrit the particles. Attrition resistance is particularly desired of a catalyst which is prepared, used, or transported in large volumes.
Further, and more importantly, the quality of petroleum distillates required to be treated has been reduced in recent years. As a result of the diminishing supply of petroleum reserves, stocks having a relatively low content of gums and other polymeric compounds are less available. Because distillates having high gum content can cause numerous problems during processing, such as fouling catalysts, it is increasingly necessary to develop catalysts which are resistant to gum accumulation and resultant deactivation.
The catalytic composite of this invention combines the desirable characteristics of having a high physical strength and resistance to attrition, the ability to convert to disulfides the mercaptans in a sour petroleum distillate at least as well as prior art catalysts, and the ability superior to prior art catalysts to resist accumulation of the gum content of the distillate being treated. The physical strength of the catalytic composite of this invention allows more severe conditions of preparation and use of the catalytic composite. The ability to sweeten a petroleum distillate having a high gum content means that the process of sweetening sour petroleum distillates can be performed more efficiently. The catalytic composite of this invention provides processors of sour petroleum distillates with an alternative useful method of treating such stocks to produce saleable products.